1. Field of the Invention
The present invention relates to a movable work support, also referred to as a scaffold, which is particularly adapted to use within a cylindrical structure, and which includes means for vertical and rotational movement of the support within the structure.
2. Description of the Prior Art
A large variety of scaffolding structures are known in the prior art for particular applications. Scaffolds provide a work surface upon which a workman or apparatus may be positioned adjacent a structure to permit work to be done on the structure. Typically, scaffolds may be classified as either those which are fixed structures which require disassembly and reassembly in order to move their location, and those which incorporate means for changing the location or orientation of the scaffold.
The closest prior art to the present invention is believed to be shown in U.S. Pat. No. 3,420,332, issued to Textor on Jan. 7, 1969. The Textor patent discloses a work support which is adapted for use within a cylindrical structure and which includes means for vertical and rotational movement of the scaffold. The Textor device includes a rigid suspension unit which is connected to the center of the top of a silo or similar structure. At one end of this rigid suspension unit is located a yoke which supports a pair of rollers positioned to bear against the inner surface of the top of the enclosure. A work platform is suspended from the suspension unit by a pair of chains which attach to opposite ends of the work platform. One of the chains extends from the suspension unit at the end of the suspension unit opposite the location of the yoke and bearing rollers. The other chain extends from the suspension unit at a point intermediate the ends of the suspension unit. The chains are thereby positioned such that the center of gravity of the work platform is located to have the point of attachment of the suspension unit to the top of the structure between the bearing rollers and the center of gravity. The center of gravity therefore applies a force which causes the bearing rollers to bear against the top of the structure within which the scaffold is being employed. The work platform of the Textor device also includes wheels which are positioned to bear against the interior of the side wall of the silo or other structure. These wheels are positioned to move the work platform further from the side wall than would otherwise be the case, and therefore causes frictional engagement of the wheels to the side wall. However, the center of gravity of the platform remains located as previously described with respect to the point of attachment of the suspension unit to the top of the structure. In operation, a workman is positioned on the work platform and is thereby located near the portion of the side wall against which bear the wheels located on the platform. The Textor device is suitable for certain structures. However, the Textor device is not operable if a structure has a top which is not smooth on the inside for the bearing rollers to move over or which has a top which is not sufficiently strong at required locations for the rollers to bear against. Some farm structures, for example, have only a tripod at the top with either a thin sheet metal covering, or no covering at all, and the Textor device could not be used therewith for both of the reasons heretofore enumerated.
A hanging scaffold for use within a cylindrical structure is also disclosed in U.S. Pat. No. 1,090,856, issued to Johnson on Mar. 24, 1914. The Johnson scaffold comprises a circular structure including wheels for centering the scaffold within the cylindrical structure. A similar device is disclosed in U.S. Pat. No. 1,284,699, issued to Johnson on Nov. 12, 1918. In U.S. Pat. Nos. 3,187,838, issued to Stewart et al. on June 8, 1965, and 3,241,634, issued to Prosser on Mar. 22, 1966, there are disclosed scaffolding structures which are positionable about the outside of a cylindrical structure.